TRANSPORTATION OF DEBRIS BY ICEBERGS 75 
of their occurrence. ‘To the south the divide is at every point much 
higher than goo feet. Unless, therefore, the ice front is conceived 
as a long projecting point occupying the center of the lake valley 
and margined by lake waters on both sides for a considerable dis- 
tance, the ice barrier should be placed comparatively remote from 
the site of the clay deposit. ‘This concept is also in accord with 
observation of tidal and marginal-lake ice fronts in Alaska—there 
is an almost straight line truncation of the ice where it is fronted 
© DOT INOICATES POINT IN 
LAME CLAY OEPOSITS FROr 
WHICHE SPECITIENS WERE 
SECUAED. 
JURNE SANDSTONE 
te-—— ABOUT 12 mILES ut 
Fic. 1.—Block diagram of the region around the southern end of Cayuga Lake, 
New York. 
by deep water. Again, the lake clay at the occurrence described 
has a thickness of at least 10 feet, and perhaps double that, with 
perfect, undisturbed stratification indicating a relatively long- 
continued period of deposition unaffected by minor oscillations of 
the ice front. 
Purpose of paper.—It is the purpose of this paper to recount the 
recovery of rock material from a limited area and depth of this lake 
clay, to indicate the amount and character of this material, to 
account for its presence, and to make certain deductions from these 
facts with regard to the character and effectiveness of the erosive 
activities of glacial ice. ¢ 
